This invention pertains to three-way precious metal catalysts which utilize an oxygen-ion conducting support material for simultaneous oxidation of carbon monoxide, hydrogen and hydrocarbon compounds and reduction of nitrogen oxides present in gas emissions from mobile or stationary fuel combustion sources, such as automotive exhaust gases or power plant gas emissions.
Supported metal catalysts are widely used for oxidation and reduction of pollutants present in gas exhausts or emissions from mobile or stationary internal combustion power generation sources. One approach to solving this gas emission problem by simultaneous oxidation of carbon monoxide and hydrocarbons and reduction of NO.sub.X compounds in exhaust gases is passing such gases through a single bed catalytic converter. The three-way catalyst used in the converter typically consists of platinum (Pt), rhodium (Rh) and sometimes palladium (Pd) deposited on a conventional .gamma.-alumina (Al.sub.2 O.sub.3) support material, which may be in either pellet or a monolithic form.
The existing precious metal catalysts for treatment of automotive exhaust gases typically uses alumina and sometimes ceria-stabilized .gamma.-alumina or lanthanum oxide-stabilized .gamma.-alumina as a support material. It is believed that the addition of ceria may promote the performance of the three-way catalyst by facilitating the water-gas shift reaction, by acting as an oxygen storage unit, and by stabilizing the gamma-alumina support against loss of surface area. But none of the known catalyst supports used for automobile exhaust gases treatment have provided any oxygen-ion conducting property. We have now found that use of an oxygen-ion conducting catalyst support material greatly improved the pollutant removal capability of previous metal catalysts without the need for increase in the catalyst active previous metal content, which makes the catalyst too costly.